Barometric Draft Control Dampers are designed for Oil or Gas Furnace applications. Oil Furnaces use a "Single-Acting" draft control to maintain a consistent vent draft by counteracting the negative pressure changes caused by temperature and barometric pressure, as well as, wind effect. Gas Furnaces use a "Double Acting" draft control. It opens inwardly to maintain a uniform draft. It can also open outwardly to spill combustion by-products in case of blocked flues or down drafts.